This invention relates to an instrument which measures the position of various points of interest in a three-dimensional space and, more particularly, to an instrument which measures the position of points along straight portions of a preformed tube. The measurements may be converted to vectors which can be used to generate instructions to a bending machine to manufacture reproductions of the preformed tube.
U.S. Pat. No. 3,944,798, to Eaton, discloses an apparatus for measuring the angles of a surface or axis of an object with respect to three reference planes. The apparatus includes a working head which may be engaged with a surface of the object being measured. The head is mounted in an articulate manner through a series of five pivoted arms to a work table. Each joint between supporting arms has a sensor or resolver which measures the relative angular positions of the arms to collectively define the position of the working head. A circuit processes the signals from the five analog sensors to calculate the relative position of the working head.
British Pat. No. 1,329,708 issued to McMurtry describes a method for making a bent pipe from a master pipe based upon measurements taken from the master pipe. McMurtry shows a measuring apparatus having a sensing head mounted for rectilinear movement in the X, Y and Z directions. McMurtry's apparatus has an arm upon which is mounted a carrier having an offset end portion. A sensing head having an outwardly opening U-shaped cross section is mounted on the offset end portion to receive the surface of the pipe. A projection of the axis of the arm intersects the axis of the sensing head at the centerline of the pipe when the surface of the pipe is in engagement with the sensing head. McMurtry obtains measurements of the centerline coordinates at two locations for each straight portion of the bent tube. The coordinates of the point on the centerline of the straight portions of the pipe are utilized to calculate a bending program.
Eaton requires five analog sensors or resolvers to acquire sufficient information to develop a bending program. McMurtry must adjust the position of the offset end or change the size of the sensing head to accommodate individual tube diameters.
Considering these drawbacks, I have developed an instrument which requires only three resolvers and engages the surface of the tube to effect an accurate measurement of the position of points along the centerline of the straight portions thereof. A single sensor or tube feeler accommodates a range of tube diameters.